This invention relates generally to spark generation and more particularly to a method and apparatus for controllably generating and shaping sparks in an ignition system or the like.
Solid-state ignition systems are known in the art. U.S. Pat. Nos. 5,065,073 and 5,245,252, the disclosures of which are hereby incorporated by reference, teach, inter alia, that improved control over the performance of an ignition system can be achieved by incorporating a solid-state switch into an ignition output circuit. As taught by these patents, the ability of a solid-state switch to be triggered at a precise time allows an ignition system incorporating such a switch to achieve controlled spark rates. It also allows such a system to generate time-varying spark sequences. In addition, as explained in the above referenced patents, since a solid-state switch can be controlled independently of the voltage level of the ignition system""s tank capacitor, an ignition system incorporating a solid-state switch can be used to deliver various amounts of energy by triggering the solid-state switch when a voltage associated with a desired energy transfer appears across the tank capacitor. This later effect cannot be achieved in older circuits using spark-gap switches since such switches fire only at a single voltage which is preset during manufacture of the spark-gap switch and will, thus, fire as soon as the voltage across the tank capacitor reaches the preset triggering level.
The ""073 and ""252 Patents also teach the desirability of waveshaping the current delivered into an igniter plug for a sparking event. For example, these patents teach that it is desirable to deliver a current to an igniter plug which initially increases at a low rate while ionizing the plug""s gap and thereafter increases at a higher rate to sustain a spark across the ionized gap. Among other things, controlling the rise time of the current in this manner maximizes the life of the solid-state switch and the igniter plug by providing such components an opportunity to pass through their transition states before being taxed with a full, high energy pulse.
As mentioned above, prior art circuits such as those disclosed in the ""073 and ""252 Patents have achieved some degree of control over spark generation. However, prior art circuits such as these, while achieving many beneficial effects, have been somewhat constrained in their ability to control spark generation by certain physical limitations. For example, it is well known that the energy stored in an ignition circuit employing a tank capacitor is described by the formula:
Energy=xc2xd*Capacitance*(Voltage)2
Thus, the energy delivered by such a circuit can be varied by changing either the charging voltage placed across the tank capacitor or the capacitance of the tank capacitor itself. There are, however, several practical limitations involved in varying these characteristics. For example, lowering the voltage levels used in the circuit requires a disproportionately large increase in the physical size of the capacitor used in the circuit to achieve similar energy levels. On the other hand, the available selection of capacitors, insulation materials, and solid-state switch components becomes limited at higher voltage levels.
The capacitance of prior art spark generating circuits is generally fixed when those circuits are constructed. In a circuit which uses a spark-gap switch the voltage is also fixed by the choice of the gap""s breakdown voltage. Thus, traditional spark generating circuits are designed to deliver a predetermined energy level, but that energy level is thereafter unadjustable. In addition, prior art circuits have not attempted to control the plume shape of sparks generated at a spark generating device.
Ignition systems have been constructed for use as test apparatus wherein the user can manually vary the energy delivered by the system by physically connecting or disconnecting multiple capacitors to achieve various total capacitance and, thus, various total stored energy. However, from a safety standpoint, the high voltage and current levels in this part of the circuit makes physically switching capacitors in or out of the circuit somewhat impractical; usually requiring power-down and physical reconnection before sparking can continue. In addition, these systems have been limited to adjusting the total energy delivered and have not provided any spark shaping capabilities or real time control over the intensity and shape of the sparks generated.
It is a general object of the invention to provide an improved method and apparatus for shaping and controlling sparks. More specifically, it is an object of the invention to provide an improved method and apparatus for controllably generating sparks wherein both the energy level and the profile over time of an energy pulse used to generate sparks at a spark generating device can be electronically adjusted to suit a given application.
It is another object of the invention to provide an apparatus which electronically switches multiple discharges into a common output for the purpose of creating an ignition spark event at a spark generating device. It is a related object to provide an apparatus wherein the total energy delivered to a spark generating device is the additive contribution of multiple discharge circuits. It is a related object to provide an apparatus which more reliably generates a significantly higher total energy output pulse than prior art circuits by using multiple independent discharge circuits which individually generate relatively lower energy outputs that are combined to achieve a high energy output pulse rather than increasing the stress on a single larger energy circuit.
It is another object of the invention to provide an apparatus which can deliver a specific level of energy to a spark generating device by intentionally discharging only a subset of the multiple discharge stages. It is a related object of the invention to provide an apparatus which selectively combines the outputs of two or more discharge stages having various output energy levels to generate final output pulses having a wide range of energy levels.
It is another object to provide an apparatus which employs a binary weighting of the values of the tank capacitors of the discharge stages to provide a greater variety of possible output energies.
It is yet another object of the invention to provide an apparatus which permits a user to adjust the voltage(s) of the tank capacitors in the individual discharge stages to scale their energy levels. It is another object to provide an apparatus which permits a user to both adjust the voltage(s) of the tank capacitors in the individual discharge stages and to select which stages to trigger thereby increasing the range of possible output levels so that output pulses having virtually any energy level (zero to maximum) can be generated.
Another object of the invention is to provide an apparatus which actively waveshapes its output pulse by timing the discharging of several discharge stages so that a pattern of overlapping, partially overlapping, or non-overlapping discharges form a waveshaped pulse for generating a spark having a given plume shape. It is a related object to provide an apparatus which generates an electrical waveform that imparts various characteristics to the physical time-varying shape of the spark plume created at a spark generating device.
It is still another object of the invention to provide an ignition system which achieves better ignition by optimizing the spark plume for best transferring its energy into the fuel mixture.
Another object of the invention is to provide a spark generating apparatus whose operation enhances the life of an associated spark generating device by controlling the spark plume to reduce the arc-induced erosion of the spark electrodes. It is a related object to provide an apparatus which ionizes the gap of a spark generating device to form a plasma using a small energy pulse, and then later delivers the remainder of the energy to the plasma to complete the spark event.
It is yet another object of the invention to provide a reliable ignition source for a variety of applications which require spark ignition, including but not limited to turbine engines, piston engines, internal combustion engines, rocket engines, open or closed burners, and any other apparatus utilizing a spark ignition system. It is a related object of the invention to provide an apparatus for generating and shaping sparks for use in devices such as spacecraft thrusters where the spark itself is the primary output, or where the spark ablates a solid material or vaporizes a liquid, to provide additional thrust. In these cases conventional xe2x80x9cignitionxe2x80x9d of a fuel does not occur, but the benefits of the invention are still applicable.
It is still another object of the invention to provide an adjustable test apparatus which permits the generation of sparks having any desired plume shape and energy level for the purpose of determining the optimum parameters (i.e., energy level, energy distribution, three-dimensional shape, spatial intensity, and duration; any or all as a function of time, if desired) of sparks generated for a particular application.
It is a further object of the invention to provide a fixed, non-adjustable apparatus for spark generation where the energy level and plume shape of the generated sparks are fixed once the apparatus is constructed, and in which only the circuitry required to generate sparks having those particular fixed characteristics are included in the final apparatus.
Another object of the invention is to provide an apparatus for generating sparks which multiplies the energy of the output pulse by firing multiple stages simultaneously.
Another object of the invention is to provide an apparatus for actively shaping the plume of sparks generated in either high-tension or low-tension ignition systems.
It is an object of the invention to provide an apparatus which can be adapted for shaping sparks in both bipolar output systems and unipolar output systems.
It is another object of the invention to provide an apparatus for generating sparks in a plurality of spark generating devices such as in a multi-cylinder or multi-combustor engine. It is a related object to incorporate pulse steering circuitry into such an apparatus so that a single output pulse may be selectively directed to any one of a group of spark generating devices in a multiple output application. It is another related object to control multiple circuits built according to the invention using common control logic circuitry to synchronize their operation in a multiple output application.
It is another object of the invention to provide an apparatus for generating sparks at a high rate sufficient for use with multi-cylinder piston engines by sequentially firing the individual output stages in a non-overlapping manner to thereby generate sequences of closely spaced sparks, where each spark is a separate (non-additive) event.
The present invention accomplishes these objectives and overcomes the drawbacks of the prior art by providing an apparatus for controllably generating sparks which includes a spark generating device; at least two output stages connected to the spark generating device; means for charging energy storage devices in the output stages and at least partially isolating the energy storage device of each output stage from the energy storage devices of the other output stages; and, a logic circuit for selectively triggering the output stages to generate a spark. Each of the output stages includes: (1) an energy storage device to store energy; (2) a controlled switch for selectively discharging the energy storage device; and (3) a network for transferring the energy discharged by the energy storage device to the spark generating device. In accordance with one aspect of the invention, the logic circuit, which is connected to the controlled switches of the output stages, can be configured to fire the output stages at different times, in different orders, and/or in different combinations to provide the spark generating device with output pulses having substantially any desired waveshape and energy level to thereby produce a spark having substantially any desired energy level and plume shape at the spark generating device to suit any application.
In accordance with another aspect of the invention, the charging and isolating means may optionally comprise a plurality of charging circuits. In such an instance, each of the output stages can optionally be assigned a separate charging circuit for charging independently of the other output stages. Employing separate charging circuits in this manner insures that each of the energy storage devices are at least partially isolated from the other energy storage devices. The use of separate charging circuits is especially useful in applications where it is desirable to charge the energy storage devices to different voltages.
In accordance with another aspect of the invention, a method for controllably generating sparks at a spark generating device is provided. The method comprises the steps of charging a first energy storage device to a first predetermined voltage (hence, energy); charging a second energy storage device which is at least partially electrically isolated from the first energy storage device to a second predetermined voltage (hence, energy); triggering a first controlled switch associated with the first energy storage device to discharge the first energy storage device to the spark generating device at a first time in the form of an energy pulse; triggering a second controlled switch associated with the second energy storage device to discharge the second energy storage device to the spark generating device at a second time in the form of an energy pulse. In accordance with another aspect of the invention, the first and second predetermined voltages, the capacitances of the first and second energy storage devices, and the first and second times can all be adjusted to generate sparks of any desired energy distribution, three-dimensional shape, spatial intensity and duration; any or all as a function of time, if desired.
These and other features and advantages of the invention will be more readily apparent upon reading the following description of the preferred embodiment of the invention and upon reference to the accompanying drawings wherein: